combine on duplicate check with insert_batch

[eluser]Unknown[/eluser]
I have a script that successfully uses CI's active record function insert_batch

I would like to combine some MySQL functionality to this, specifically ON DUPLICATE KEY ....
Since the insert_batch function just takes two parameters (table name, and an associative array of the batch key/value pairs), how can I get this added? Writing the ON DUPLICATE KEY {do something} code is already done, I just don't see an active record function to add this when using the batch_insert function.